<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

</head>
<body>

    <button>点击发送请求</button>
    <div class="result"></div>
    <script>
        const btn = document.getElementsByTagName('button')[0];
        const result = document.getElementsByClassName('result')[0];
        btn.onclick = function(){
            const xhr = new XMLHttpRequest();
            xhr.open('POST','http://127.0.0.1:3000/server?a=100&b=200&c=300');
            xhr.send();
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4){

                    if((xhr.status >= 200 && xhr.status<300)||xhr.status === 304){
                        console.log(xhr.responseText);
                        console.log(xhr.status);
                        result.innerHTML=xhr.responseText;
                    }else{
                        console.log(xhr.status);
                        
                    }
                }
            }
        }

    </script>
        <style>
            .result{
                width: 600px;
                height: 600px;
                border: 2px solid red;
                margin: 20px;
            }
        </style>

</body>
</html>